Automobiles are the most common vehicles in daily lives and at least include left side mirrors, right side mirrors, and rearview mirrors for providing left rear, right rear, and central rear images to drivers by reflection. Nonetheless, the field of view provided by these mirrors for drivers is limited. In addition, for providing drivers with wider field of view, the adoption of convex lenses is indispensable. A convex lens forms shrunk and erect virtual images. Thereby, as a close obstacle is imaged by a convex lens, an illusion that the obstacle looks farer will result. As a consequence, it is difficult for drivers to estimate the real distance to the obstacle.
When automobiles are running on roads, due to limited field of view, errors in estimating distances, spiritual fatigue, or others' non-law-abidance, the safety of the lives of drivers and passersby are both threatened. In order to improve safety, many passive safety equipment pieces have become standard; active safety equipment pieces are continuously developing under the endeavor of various major automobile manufacturers.
Among the current technologies of active safety equipment, some safety alarm devices allowing real-time warning on users are provided, including, for example, reversing radars using signal transmitters and receives, or audio reminding equipment when other objects approach the car. Unfortunately, for drivers, some visual dead spaces of automobiles still exist. In particular, while reversing a car, a large portion of the driver's field of vision is blocked by the car body and forming the visual dead spaces. Consequently, drivers are unable to aware the existence of the obstacles or hollows in roads close to the car body.
According to some current technologies, a camera is installed outside a car. Images are captured by the image extraction device and displayed on the display device in the car for driver's reference. Unfortunately, the range of the images captured by the image extraction device is limited. Besides, the image extraction device should be fixed at the same location. Thereby, the capturing range for images cannot be varied according to turning angle of the car, leading to the generation of some visual dead spaces. Furthermore, the images taken by the image extraction device are planar images, making the drivers difficult to master the distance to obstacles according to the images. Some current vendors will add reference lines in the images as the reference for judging distance for drivers. Nonetheless, this method only gives approximate distances for drivers. It is not possible to acutely just the distance between an obstacle or a hollow in the road and the car body.